Microorganisms are ubiquitous, that is, they are found everywhere. They have been found to survive extreme conditions such as low water availability, high salinity, high temperature, high pH, high pressure, intense solar radiation, etc. Thus, microorganisms that survive these extreme conditions are referred to as extremophiles. They are classified on the basis of the main characteristics of their environment, this classification include psychrophiles, thermophiles, hyperthermophiles, halophiles, acidophiles, alkiphiles, barophiles, etc.
Extreme habitats are environments that contains conditions that are regarded very hard for survival of life, these conditions include high or low temperature, high or low pressure, high or low of oxygen or carbon dioxide content, high levels of radiation, high or low pH, high salinity, presence of petroleum, sulphur or other toxic substances. Examples of these extreme habitats are deep seas, deserts, atmosphere, etc.
Extremophiles have some adaptive features which makes them to be able to survive and thrive in the extreme environments. The discovery of extreme environments and extremophiles has made more commendable the search of life outside the earth and has brought about biotechnological applications (Rothschild and Mancinelli, 2001).
Extreme habitats are environments that experience regular or irregular exposure to one or more environmental factors such as temperature, pH, salinity, osmolarity, desiccation, radiation, oxygen, carbon dioxide, water, etc. (Seufferheld et al., 2008). Some extreme habitats are, however, due to man activities such as discharge of pollutants such as sewage, industrial effluents, petroleum or other toxic substances into the environment (Selbmann, 2013). Therefore, extreme habitats are considered selective, hostile and hard for major life forms to survive due to these conditions.
Examples of extreme habitats include the geographical poles (polar regions), very arid deserts, volcanoes, deep ocean trenches, upper atmosphere, Mt Everest, outer space, etc. Organisms that live in these conditions are usually very well adapted to their living circumstances, which is usually a result of long-term evolution.
The temperature in polar regions is very low therefore the number of organisms that can survive this low temperature is low, though some organisms can survive and thrive in this extremely cold environment.
Deserts have extreme temperature and dry climate, e.g. the Atacoma desert which is one of the oldest, driest and hottest desert, the Antarctic dry valleys which is the coldest and driest inhabit organisms such as cyanobacteria, algae and fungi, thigh these organisms are photosynthetic but they are able to adapt to the extremely dry conditions.
The deep sea has high pressure and low temperature (1-2°C). In the hydrothermal vents (the sea floor), the ph range from 3-8, the temperature may be as high as 400°C but the water remains liquid due to the high pressure. Deep sea is a habitat for psychrophiles (organisms that thrive in low temperature), hyperthermophiles (organisms that can survive very high temperature) and piezothermophiles (organisms adapted to high pressure).
These environments are high in salt concentration. Examples of these environments are natural lakes (e.g. Great Salt lake), evaporation ponds, salt flats and deep sea hypersaline basins. The halophiles are the organisms that can thrive in these environments.
Ice, Permafrost and Snow
Some organisms have evolved so as to adapt to these habitats. Organisms such as bacteria, protozoa and algae inhabit liquid brine (high saline water) which is contained in the pockets of the ice. Some other organisms are not ice lovers but they can survive the condition because they possess adaptive features that enable them to survive.
The atmosphere is considered an extreme habitat for microorganisms. Factors that make the atmosphere an extreme environment include desiccation, humidity, temperature and radiation. Microorganism that can survive this habitat have the ability to withstand these factors.
The ability of extremophiles to survive exposure to conditions of outer space has raised the possibility that life exist outside the earth.
Anthropogenically impacted habitats
These are extreme habitats caused by human activities such as oil impacted habitats, mine tailings, pollution by heavy metals or organic compounds or toxic substances, etc. Microorganisms that can survive these habitats are able to degrade these substances.
Extreme conditions does not only include physical extremes e.g. temperature, radiation or pressure) and geochemical extremes (desiccation, salinity, pH, oxygen species or redox potential) , or anthropogenically impacted habitats, it also includes biological extremes such as nutritional extremes (oligotrophic-a habitat with very low nutrients), and extremes of population density (competition), parasites, prey, etc.